I have iincreased my bunkering over the years, because good bunkers help aesthetics, and that is important in marketing, like it or not. I am not "selling out" because I happen to like that look of random bunkers in random placements, a la MacKenzie.
I usually end up with 60-75, for cost and maintenance reasons. I have no formula, but do like to mix in a few bunkerless holes, some featuring small bunkers, some large, some few, some many, etc. Without my internal checks and balances, I couldn't hold myself back from becoming a Steve Smyers, who often has 100 bunkers or more on his courses, and they look great!
Also important, IMHO, is mixing different difficulties in bunkers. A few weeks ago, I posted that at one time, I felt it would be neat to have very few bunkers, but make each deep enough to really signal strategy. I have drifted to more bunkers, but would really like to have at least a few holes, where one very deep bunker on one side of the green sets up the entire play. Another hole might have a dozen, but none that really scare you.
While I have often doubted the greatness of the Eden hole, as compared to many, I do recall Wind describing it as seeing and avoiding the deeper Strath bunker in front, and possibly pushing yourself too far left into the other bunker as a result.
Dick Nugent used to use the term "Master Bunker." Whether there is one deep one, or one deep bunker and several not so difficult ones, he tried to create that. Over time, the golfer would learn which bunkers to avoid, and start to welcome being in one of the supplementary hazards, knowing it was easier. Of course, it may not be depth that makes it a master bunker, it may be a gathering quality which creates the fear in the golfer.
Having said that, it is very possible to overlitter a hole with too many decorative bunkers. I won't name them, but a few of my holes do have bunkers that could easily be removed, and in this economy, probably will. I have had a few clients call me to ask whether they could remove X bunker for maintenance reasons, and when thinking in that mode, its not hard for me to think of several that are superfulous.
It stikes me reading Tom MacWood's post that there may not have been quite the disconnect from the depression until after WWII that we often suppose, because the older architects died, and didn't practice for so long until RTJ came back strong in 1950 or so. Assuming they could read, I think Tillie's articles and PGA reports had an influence among architects away from the randomness of, say, Cypress Point, and towards the "make every bunker count for the good player" mentality that dominates until this day.
There is something to be said for every bunker influencing play of the best players, and letting the duffers enjoy the challenge of hitting the ball in the air and reasonably straight.....